Firearm thumb support



FIG. 1 is a perspective view of a firearm thumb support.

FIG. 2 is another perspective view thereof.

FIG. 3 is a side view thereof.

FIG. 4 is a front view thereof; and,

FIG. 5 is a side view of the firearm thumb support in use configuration with an unclaimed firearm.

The broken lines in FIG. 5 depict an unclaimed rifle included for environmental context and form no part of the claimed design. 

CLAIM The ornamental design for a firearm thumb support, as shown and described. 